Patent Documents 1 and 2 below disclose techniques of using cooled wind from a fan to provide efficient and forcible air-cooling for a heatsink to which a semiconductor device is attached.
Patent Document 1 provides a heat dissipation plate to a portion above the top surface of a heatsink to which a semiconductor device is attached, and allows cooled wind (outer air) suctioned by a fan to pass through the space between that heat dissipation plate and a printed circuit board.
Patent Document 2 forms hollow spaces in a plurality of bus bars, and allows cooled wind (outer air) suctioned by a fan to pass through the formed hollow spaces.
The techniques disclosed by Patent Documents 1 and 2 use a heat dissipation plate or a bus bar for the entire air channel (or part of it) of the cooled wind from the fan, resulting in a larger size or a higher price for the device, which is problematic.    Patent Document 1: Japanese Laid-open Patent Publication No. 2009-044842    Patent Document 2: Japanese Laid-open Patent Publication No. 2008-166531